Calorie Restriction Diet
Caloric restriction is the practice of reducing consumption of calories in a diet by replacing high calorie foods with low calorie foods that still contain the necessary vitamins and minerals a body needs. It has been found that caloric restriction extends the lifespan and slows down age-related chronic diseases in rats, fish, flies, worms, and yeast. Caloric restriction decreases metabolic rate and oxidative stress, improves insulin sensitivity, and alters neuroendocrine and sympathetic nervous system functioning in animals. It is unknown whether prolonged caloric restriction increases lifespan in humans.
Since the 1930s it has been known that a diet restricted in calories — at least 30 percent fewer calories than normal, but otherwise rich in nutrients, can dramatically extend the life span of experimental animals in over two thousand studies in a wide variety of species (not including primates yet), and also appear to be more resistant to age-related diseases. In fact, caloric restriction appears to delay normal age-related degeneration of almost all physiological systems. While the effectiveness of this anti-aging regimen is likely far greater than others currently available, the difficulty of the regimen is also far greater in order to change people’s eating habits. Investigators are exploring the question of whether drugs might mimic its effects.
Although Caloric Restriction is the only known intervention shown to prolong life, how it works is not clear. Because cutting down on calories slows metabolism, and free radicals are byproducts of metabolism, caloric restriction may reduce oxidative damage to cells. Calorie restricted animals also have less glucose circulating in their blood. This may reduce “glycation” and lessen the potential for protein crosslinking, a biochemical process implicated in cellular aging. And because caloric restriction lowers body temperature slightly, cells may sustain less genetic damage than at normal body temperature. In addition, scientists speculate that caloric restriction preserves the capacity of cells to proliferate, and that it keeps the immune system functioning at youthful levels. Caloric restriction also may work through other mechanisms. It may, for instance, influence hormonal balance, cell senescence, or gene expression by triggering alterations in genetic activities. Or, it might work through a combination of all of these mechanisms, plus other factors.
The dauer pathway in C. elegans is an alternative developmental pathway that results in a significant life-extension (Klass and Hirsh, 1976). In the dauer pathway, which can be activated by starvation and hence may be analogous to Caloric Restriction.
In a current National Institute of Health study at the University of Wisconsin, a group of monkeys is under caloric restriction, consuming 30% fewer calories each day over the past 20 years than the other monkeys in the experiment. The purpose of the study is to find out whether caloric restriction makes this group of monkeys healthier and extends their lives. Reporters from 60 Minutes visited the facility and observed major differences in the overall health of the monkeys. Those on caloric restriction are thinner, look younger, have shinier coats, and fewer have arthritis. In contrast, many of those on a normal monkey diet have diabetes and more have heart disease and cancer. The researchers believe that eating a lot of food turns the sirtuin gene off, and that caloric restriction turns it on.
Calorie Restriction and Rate of Living Theory of Aging
As previously mentioned, caloric restriction (CR) is one of the most important discoveries in aging research. Although the mechanisms behind CR remain a subject of discussion, since it involves a decrease in calories, one hypothesis put forward by George Sacher is that maybe CR works by delaying metabolic rates, in accordance with the energy consumption hypothesis. Body temperature is crucial to determine metabolic rate since the rate of chemical reactions rises with temperature. One common feature of animals, such as mice, rats, and monkeys, under CR is a lower body temperature which is consistent with the energy consumption hypothesis. On the other hand, some studies in rodents suggest that CR can extend lifespan without reducing metabolic rate. For example, some evidence indicates that mice under CR burn the same amount of energy as controls, suggesting they have similar metabolic rates. These studies, however, remain controversial in the way metabolic rate is normalized to metabolic mass. An alternative hypothesis is that CR shifts metabolic pathways. More recent results suggest that previous studies used unreliable estimates of metabolic mass in their calculations and indeed CR changes metabolic rates, supporting the rate of living hypothesis, but the debate has not been settled.
